SIMOX is a technique that is employed in fabricating SOI substrates which can be used in the manufacturing of ICs. SIMOX typically involves using high-energy ions to implant a large dose of oxygen ions beneath the surface of a bulk Si wafer. Upon high-temperature annealing, the implanted oxygen forms a continuous buried oxide (BOX) region which electrically isolates the Si at the surface (i.e., the superficial Si layer). Typically, prior art SIMOX processes have been used to fabricate SOIs with a superficial Si layer and a BOX thickness of several thousand angstroms.
Conventional SIMOX processes include one of the following methods:
(i) a high-dose oxygen implantation (greater than about 4E17 cm−2) step followed by annealing at temperatures of greater than about 1300° C. in an inert ambient such as Ar or N2 that contains less than about 5% oxygen.
(ii) a high-dose oxygen implantation (greater than about 4E17 cm−2) step followed by annealing at temperatures of greater than about 1300° C. in an inert ambient such as Ar or N2 that contains a much higher content of oxygen than in method (i). Typically, the oxygen content used in the annealing step in this method is between 30–40% which is employed to promote internal thermal oxidation.
(iii) Combining base oxygen implant of greater than about 2E17 cm−2 and room temperature implant (typically greater than about 1E15 cm−2) followed by annealing in an inert ambient that contains oxygen in a concentration range of from about 8 to about 70%.
The conventional SIMOX processes mentioned above each suffer from the same problem in that the prior art SIMOX processes produce a superficial Si layer that contains tiles or divots. A pictorial representation of a prior art SOI substrate (top-down view) is shown, for example, in FIG. 1A. Specifically, FIG. 1A shows a portion of superficial Si layer 14 which lies atop a buried oxide region (BOX) that is not shown in this drawing. Note that in this drawing the superficial Si layer includes discrete tiles 16 across the entire surface of the superficial Si layer.
FIG. 1B is a pictorial representation (through a cross-section) of a prior art SOI substrate. This substrate includes bottom Si layer 10, BOX region 12 and superficial Si layer 14. Note that in this drawing, divots 18 are shown in the surface of the superficial Si layer. Divots 18 are formed substantially at the point wherein the horizontal lines and the vertical lines shown in FIG. 1A intersect each other.
Typical optical inspection tools such as the KLA Tanker optical tool that operate with green to white light is inundated by the tile or divot features such that it is difficult to inspect other process induced features or defects which are much lower in density and can severely impact circuit yield.
To date, there are no satisfactory means for removing the tile or divot features that do not involve physically removing a portion of the superficial Si layer. Thus, there is a need for developing a new and improved SIMOX process in which the number of tile or divot features formed in the superficial Si layer is substantially reduced.